This invention relates generally to automotive diagnostic test equipment and particularly to computer-based equipment for testing and evaluating internal combustion engines.
The prior art discloses numerous automobile engine diagnostic testing devices that are computer based. One diagnostic tester, identified as the Sun Electric Corporation Model 2001, is described and claimed in U.S. Pat. No. 4,125,894, issued Nov. 14th, 1978, which is incorporated by reference herein. With such a tester, selected analog signals are gathered from the engine under test by one or more suitable probes connected to the engine and the analog signals received therefrom are manipulated, processed and compared with factory specifications for the engine. The data is also displayed on a raster scan cathode ray tube (CRT) display and a print out of test results is also provided.
A recently introduced diagnostic tester that is IBM compatible is the Sun Electric Corporation Model MCA 3000. The MCA 3000 is capable of receiving and processing engine test signals at significantly higher speeds than prior art testers. The high speed of the MCA 3000 is due largely to its data acquisition system (DAS). With the DAS, analog data and test signals obtained from the engine under test are converted by an analog to digital (A/D) converter and stored in an A/D random access memory (RAM), without the intervention of the main system microprocessor or its address/data bus. As fully described and claimed in co-pending application Ser. No. 148,973, flags that identify the beginning of an event, such as a cylinder firing, a cylinder #1 firing, a solenoid dwell cycle and the like are incorporated, where appropriate, in the output of the A/D converter for identifying the data. Sixteen bit digital words are used, eleven bits for signal magnitude, one bit for the sign (polarity) of the magnitude and four bits are made available for use as flags.
In co-pending application Ser. No. 148,972, a parity checking routine is run to identify flags in the digital words in the A/D memory. Bit masking techniques are used to find and to reset the flags when returning the data to memory and information about the location and types of flags is stored in pointer arrays established by the system microprocessor controller.
The present invention utilizes a card slot reserved for a read only memory (ROM) cartridge in an IBM compatible PC system to add a dual ported 128 kilobyte RAM memory. The RAM memory can be written to by the DAS system as well as accessed by the system microprocessor controller. A standard single ported 128 kilobyte RAM is used in conjunction with a pair of buffers to control access to the RAM from the DAS system and the system microprocessor. With the use of the dual ported RAM, the DAS system can operate substantially independently of the system microprocessor in acquiring, converting to digital format and flagging of engine test signals. Thus the system microprocessor and its resources need not be burdened with the task of engine test data acquisition and overall system speed is significantly increased. The dual ported A/D RAM also effectively increases the total system memory available to the microprocessor.
It will be appreciated that the present invention is independent of the inventions in the co-pending applications, although significant additional benefits result from utilization of all of the inventions in a single system. While a system with all inventions will be generally described herein, but those portions that relate to flag generation and identification are more specifically described and claimed in the respective co-pending applications.